An example of a technique related to a wide-area load balancing technique for allocating packets among a plurality of server apparatuses is a wide-area load balancing scheme using a DNS (Domain Name System) specified in IETF (The Internet Engineering Task Force) RFC (Request for Comments) 1034. According to this wide-area load balancing scheme, different IP (Internet Protocol) addresses are assigned to a plurality of servers with the same host name. A terminal accessing the servers has a DNS cache in which the host name is associated with the IP address of one of the servers. When an application operating on the terminal accesses the servers, the host name is specified as a destination, and the terminal is allocated to one of the servers in accordance with the DNS cache.
Another example of a technique related to the wide-area load balancing technique is a wide-area load balancing scheme using NAT (Network Address Translation) specified in IETF RFC 1631. According to this wide-area load balancing scheme, different IP addresses are assigned to servers providing the same service. The IP addresses are referred to as the “actual IP addresses” of the servers. For these servers, a single IP address is visible to the terminal. This IP address is assigned to a NAT apparatus. The IP address visible to the terminal is referred to as a “virtual IP address”. The NAT apparatus has a NAT table in which the virtual IP address is associated with a plurality of actual IP addresses. When receiving packets destined for the virtual IP address from a terminal, the NAT apparatus refers to the NAT table to select, for example, a server with the lowest load, and translates the destination address of the packets into the actual IP address of this server.
There is known a related technique in which a plurality of servers is connected to different VLANs, and the load condition of each of the servers is detected. The VID of packets from an information terminal is converted depending on the load condition of each server or the like to switch a server to be connected to the information terminal.
There is known another related technique in which, when a client transmits a request for access to information to a GW, the GW manipulates a DA/SA field in an IP header of an IP packet for encapsulation. The GW thus transfers the request for access to information to a server selected from a group of servers.
Related art is disclosed in Japanese National Publication of International Patent Applications No. 2003-234752 and 10-84385. Related art is also disclosed in IETF RFC 1034 (1987) and IETF RFC 1631 (1994).